Monday, 14 October 2019

Breadboarding/testing dc inverter

Nice smooth startup

Breadboarding/testing dc inverter with 5532 op amp and a simple Frequency Generator with arduino ( with passive LP and HP before op-amp) .

And with this last stage, i think i got a nice buffered line-level output for the Effects chain/dubsiren design.
It boiled down to the choice of either TI LMC7660, the Microchip TC1044 or this one. As it is audio and op-amps i think the compromise was the 1054, which can deliver up to 100mA, tuned slightly faster to reduce too much noise passing to the audio ( i will regulate both rails anyway from a higher voltage dc source like a 12 Volts average wall adapter).
Saves me messing about with AC centre tapped transformers.
And definitely did not want to rely on capacitive coupling alone, as not safe enough . 100 ma should allow me up to two 5532's for stereo in and stereo out buffers.

555 example circuit

For much simpler needs , a 555 can be useful as dc inverter , but not necessarily with audio beyond some guitar pedals designs maybe. 50mA unregulated, maybe 20 mA regulated. And it is load susceptible...

Filter used with arduino PWM-dac 
low pass we can calculate : 470 ohms resistor and i used 220nF .1/ (2pi*R*C) = 1539.2160840608833246507133788444 Hz cut off freq
Same for high pass :1K resistor and1uF capacitor 1/(2 pi *1000*0.000001) = 159.154943092

Arduino PWM out( @15625 Sampling) producing a 30 hz 
out through filter ... mad distortion an phase issues
"But you could low pass before the op-amp and couple it with HP
 after the buffer to improve the situation" . Yes i could... 
but do i want to in this case ? Maybe in another.
And here is why : It peaks at 1.7v !! A well worth compromise in a design
with an atmega 328 or similar

Pic from

Friday, 23 August 2019


New boards arrived for next dub siren/delay and EQ/Reverb combos
Also got me a new T4 @600mhz . Paul, @ pjrc done it again...

Saturday, 6 July 2019

Testing du'B Siren

Clicking one of the buttons in the the applet seems to work for most browsers
Use the app surface like a pad ( mouse or touchscreen)

Friday, 20 July 2018


After bitbanging a quick library, and some head scratching, i seemed to have solved all my problems for now...